1. Field of the Invention
The present invention relates in general to a so-called "boiling liquid engine cooling system" wherein the coolant is boiled, so as to make use of the latent heat of vaporization thereof, and the coolant vapor used as vehicle removing heat from the engine, and more particularly to a control system for such cooling system by which a radiator fan is controlled to suppress suddent violent boiling of coolant in the coolant jacket of the engine.
2. Description of the Prior art
Hitherto, a so-called "boiling liquid cooling system (viz., evaporative cooling system)" has been proposed for achieving cooling of an internal combustion engine. This type cooling system basically features an arrangement wherein a liquid coolant (for example, a mixture of water and antifreeze) in the coolant jacket of the engine is permitted to boil and the gaseous coolant thus produced is passed out to an air-cooled heat exchanger or radiator where the gaseous coolant is cooled or liquefied and then circulated back into the coolant jacket of the engine. A radiator fan is used for promoting the function of the radiator. Due to the effective heat exchange achieved between the gaseous coolant in the radiator and the atmosphere surrounding the radiator, the cooling system exhibits a very high performance.
However, as will become apparent as the description proceeds, the hitherto proposed cooling systems have suffered from the drawback that violent boiling of coolant in the coolant jacket tends to occur just after operation of the radiator fan. In fact, upon energization of the radiator fan, the vapor condensation ability of the radiator is instantly increased by virtue of the cooling air flow produced by the radiator fan thereby instantly reducing the pressure in the coolant jacket of the engine. This pressure drop induces a sudden violent boiling of coolant in the coolant jacket and thus forces the liquid coolant to flow into the radiator through the vapor outlet. As is known, collecting the liquid coolant in the radiator reduces the effective heat exchange area of the same and thus lowers the performance of the same.